1. Field of the Invention
The present invention relates to fixing devices, and especially relates to a fixing device for fixing a workpiece defining a hole therein.
2. Description of Related Art
In machining or testing a workpiece, it is important to fasten the workpiece, which directly affects an accuracy of machining or testing.
For a workpiece defining a hole therein, which needs to be fastened via the hole, it is typically fastened by one of two ways.
Referring to FIG. 1, in one way, the workpiece 1 is clamped by two mandrels 2, with heads of the mandrels 2 partly inserted into the hole from opposite sides of the workpiece 1 respectively. However, in this way, the hole of the workpiece 1 should only be a through hole or the workpiece 1 should has two holes having a same axis and defined at opposite sides of the workpiece 1, and the workpiece is often skewed when clamped because a height H1 of one of the mandrels 2 may not equal to a height H2 of the other one of the mandrels 2.
Referring to FIG. 2, in the other way, the workpiece 1 is fastened by a mandrel 4, with a head of the mandrel 4 being inserted into the hole of the workpiece 1. However, because the hole of the workpiece 1 may not be accurately machined, a size of the hole may be greater or smaller than the head of the mandrel 4. When the size of the hole is smaller, the head of the mandrel 4 cannot be inserted into the hole. When the size of the hole is greater, a clearance can be formed around the head of the mandrel 4 in the hole, which leads to the workpiece 1 not being securely fastened.
What is needed is to provide a fixing device for fastening a workpiece with a hole therein.